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James Webb is fully deployed

nasa.gov

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Re: James Webb is fully deployed

#331

Post by dTal »

Dayshine wrote: post #259
divbzero wrote: post #232

Earlier quoted context omitted.

Since L2 is an unstable equilibrium, won’t there also need to be routine adjustments throughout the mission?

Does anybody know exactly how unstable L2 is? I've seen lots of people talk about how some Lagrange points are stable and others are unstable, but I've never been able to find a source for how much this matters. How long would it take for Webb to move so far off L2 that we can't communicate with it anymore, or for it to be at risk of being completely thrown out of orbit to the point that it would impact earth or the…

The failure mode of straying too far from L2 is the inability to shield the highly sensitive optics from both the Earth-Moon system and the Sun simultaneously.

Re: James Webb is fully deployed

#332

Post by phs2501 »

WalterBright wrote: post #320
terramex wrote: post #160

Earlier quoted context omitted.

It matters a lot, L2 is unstable point so if it ventures beyond L2 there would be no way to bring it back and it would enter a heliocentric orbit. Communication between Earth and telescope would become impossible after some time as gimballed antenna can only rotate so far and stray light reflected from Earth would limit its field of view. Due to that JWST will always be on 'close side of L2' and technically in slow f…

> as gimballed antenna can only rotate so far That's a fixable design problem. Or you can rotate the telescope. > stray light reflected from Earth would limit its field of view What? The earth and the moon are nearby anyway. What about that reflected light? And heck, what about the sun limiting its field of view?

Actually you can't rotate the telescope; they managed orientation even through the launch because if some of the science instruments get pointed towards the sun for too long they'll be destroyed. Now that it's deployed it's even more important that the cold side stays cold.

Re: James Webb is fully deployed

#333

Post by [deleted] »

jl6 wrote: post #192

More great news. Congratulations to all who have worked on the project. I understand the reasons for not putting a camera on or near the JWST, but I’m still a little sad that we’ll probably never get to see the thing in situ in all its operational glory. Maybe one day when it finally expires, we can launch a “sample return” mission to tow it back.

[deleted]

Re: James Webb is fully deployed

#334

Post by messe »

sandworm101 wrote: post #299
jazzyjackson wrote: post #263

Earlier quoted context omitted.

I’m sure if we ever have sufficient technology to build a city on the moon, the first museum exhibit will be a captured JWST

No. The museum will be built atop its first exibit: tranquility base. See Futurama s01e02.

For the sake of correctness, Tranquility Base is not where the museum is built upon in Futurama S01E02; you must be misremembering. In fact, the moon landing site is considered lost at the beginning of that episode.

When it's later found in the episode, it's found with the lunar ascent module still attached. Because the astronauts ascended in this module, only the descent modules should be there, so you might at first think that this is a blatant mistake on the part of the writing staff and you might hope someone was fired for that blunder[1]. However, if you pay close attention, there's a plaque behind Leela while she's in the ascent module that states "Lander returned to this site by the Historical Stickler's Society."[2]

[1]: https://www.youtube.com/watch?v=FTxw5nQX7SA [2]: https://www.reddit.com/r/futurama/comments/91kssj/i_didnt_wa...

Re: James Webb is fully deployed

#335

Post by sandworm101 »

messe wrote: post #334
sandworm101 wrote: post #299

Earlier quoted context omitted.

No. The museum will be built atop its first exibit: tranquility base. See Futurama s01e02.

For the sake of correctness, Tranquility Base is not where the museum is built upon in Futurama S01E02; you must be misremembering. In fact, the moon landing site is considered lost at the beginning of that episode. When it's later found in the episode, it's found with the lunar ascent module still attached. Because the astronauts ascended in this module, only the descent modules should be there, so you might at firs…

My bad. I do remember the issue re the assent module, and the sign, but forgot that they escaped into the lander after leaving the dome.

Re: James Webb is fully deployed

#336

Post by GoOnThenDoTell »

terramex wrote: post #160
WalterBright wrote: post #134

Earlier quoted context omitted.

Being a telescope, what matters is where it is pointing, not where it is.

It matters a lot, L2 is unstable point so if it ventures beyond L2 there would be no way to bring it back and it would enter a heliocentric orbit. Communication between Earth and telescope would become impossible after some time as gimballed antenna can only rotate so far and stray light reflected from Earth would limit its field of view. Due to that JWST will always be on 'close side of L2' and technically in slow f…

Could they put up some relay sats?

Re: James Webb is fully deployed

#337

Post by WalterBright »

tokai wrote: post #219
WalterBright wrote: post #198

Earlier quoted context omitted.

I've met Sagan (he came by our dorm for conversation and dinner with the students). He was a great man. He was wonderful to talk to. He has made great contributions to science. He deserves all the credit and accolades you mentioned. But I doubt he ever set foot in a machine shop. Making things is an entirely different skill.

Machine shop experience is not related project cost estimations.

Sorry, I'm not buying that. But that notion might be one reason why government projects cost so much.

I've taken apart cars many times. I know when I'm being fed a baloney sandwich when taking my car in for service, and use that to pare down the estimate sometimes as much as 50%.

(For all the women who rightly complain about being scammed by auto mechanics, I can vouch for them doing their best to scam me about 75% of the time.)

Re: James Webb is fully deployed

#338

Post by dTal »

ak217 wrote: post #159
WalterBright wrote: post #72

What puzzles me is the maneuvering fuel. When that fuel runs out, the telescope can no longer orient itself. This ended the life of the Kepler telescope. But aren't there other ways to orient in space? 1. use pressure from the solar wind 2. have 3 electric motors on 3 axis. Wouldn't spinning those motors rotate the craft? Electric power to do it would come from solar panels, giving it plenty of fuel.

JWST, like many other spacecraft, has reaction wheels to orient itself. The reason Kepler ran out of fuel when it did was that it was expending more maneuvering fuel for attitude control because two of its four reaction wheels failed. Hubble and the ISS also had similar failures. We're getting better all the time at building more reliable components (including reaction wheels and cryocoolers) though. Until a few year…

Perhaps in a future design the reaction wheel could be unloaded by solar rudder, reducing the need for maneuvering fuel (although station keeping fuel would still be required without an outright solar sail).

edit - apparently they do do something like this? https://news.ycombinator.com/item?id=29857031

Re: James Webb is fully deployed

#339

Post by microjim »

ttul wrote: post #4
microjim wrote: post #2

Great news! I’m happy about this. Just curious - had this mission critically fail, how likely would we be to simply try again? Who needs to approve the cost for that? Would it be politically important to succeed currently?

I don’t think there was a way to fix it remotely. It would just do minor science missions with whichever instruments actually worked.

Sorry - by ‘try again’ I meant build a new one and launch it

Re: James Webb is fully deployed

#340

Post by bopbeepboop »

JohnBooty wrote: post #208
daveslash wrote: post #204

Earlier quoted context omitted.

RE>> "I understand the reasons for not putting a camera on or near the JWST" What are the reasons? I'm sorry ~ I'm ignorant on the topic, but I'd love to learn more. Why/what are the reasons?

Great blog post from NASA themselves explaining it: https://blogs.nasa.gov/webb/2022/01/06/why-doesnt-webb-have-... the post is really not very long and I would suggest getting it straight from the horse's mouth, but for those not willing to devote a click here are arguably the most relevant bits! "deployment surveillance cameras would not add significant information of value for engineering teams commanding the spac…

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